The invention relates to a multi-purpose professional trimmer, edger, and sweeper that may be used with or without a support cart and with or without an enhanced inertia head. With the support cart it can have many of the advantages of a conventional lawnmower, while still retaining the advantages of string trimmers. In the power devices according to the invention, the basic configuration of the string (line) that is used according to the invention is as disclosed in U.S. Pat. No. 5,761,816, U.S. application Ser. No. 09/243,786, filed Feb. 3, 1999, and U.S. provisional application Ser. No. 60/103,549, filed Oct. 8, 1998, the disclosures of all of which are hereby incorporated by reference herein.
By practicing the invention it is possible to have optimum operation of a string trimmer for cutting vegetation, and also allow the string trimmer to be used as a blower or sweeper, and when in the blower or sweep mode still allowing it to be used as an edger. When the string trimmer is mounted on a cart it can be precisely positioned to take the place of a lawn mower, to do precise edging or trimming, or to accomplish a number of other objectives. When used as a blower in addition to moving vegetation from areas where it is not wanted (such as on sidewalks, patios, driveways, or the like) it can provide a cooling flow of air for the operator.
According to one aspect of the present invention a string trimmer is provided comprising: An engine or motor. A head operative connected to the engine or motor. An aerodynamic line connected to the head and having a long beam axis having a pitch angle. A shaft extending between the engine or motor and the head. And a gear box with at least two different gearings operatively connected between the engine or motor and the head for changing the gear ratio depending upon the pitch angle.
According to this aspect of the invention the engine or motor and gear box are preferably constructed so that for a first gear box gearing the head has a rotational speed of between 2500-6000 rpm, and for a second gearing the head has a rotational speed of over 6000 rpm. The string trimmer may further comprise an air scroll and debris shield, which functions as a debris shield when the aerodynamic line is used to cut vegetation, and which functions as an air scroll when the trimmer is used as a blower.
The string trimmer may also comprise at least one detented trigger which controls the energy supply to the engine or the motor. By controlling the energy supply to the engine or motor it is meant that the flow of fuel or electrical current to the engine or motor is controlled. For example, the string trimmer may further comprise a handle mounted on the shaft, a first detented trigger having at least three operational positions mounted on the shaft for controlling the energy supply to the engine or motor, a second handle mounted on the engine or motor on the opposite portion thereof from the head, and a second detented trigger mounted on the second handle for alternatively controlling the energy supply to the engine or rotor. The string trimmer may be mounted on a cart, as described hereafter.
The string trimmer may also further comprise means for changing the pitch angle of the aerodynamic line from a first pitch angle which is between about 0-10xc2x0, and a second pitch angle which is between about 15-45xc2x0 upward. The means for adjusting the pitch angle may comprise distinct first and second cartridges mounted to said heads, the first cartridge mounting the aerodynamic line so that it has a predetermined pitch angle between about 0-10xc2x0, and the second cartridge positively mounting the aerodynamic line so that it has a pitch angle between about 15-45xc2x0 upward, the first and second cartridges being alternatively mounted to the head and shaft. The invention may comprise a first head having a polar moment of inertia of between about 1.6-2.4 inch pounds second squared. When the engine or motor comprises a gasoline engine, the gear box has a first gear ratio so that the ratio of the engine speed to the head speed is about 1.5 or less. When the engine or motor comprises a battery powered motor, the gear box has a first gear ratio so that the ratio of engine output speed to head speed is greater than 1.4.
According to another aspect of the present invention a string trimmer is provided comprising: An engine or motor. A head operative connected to the engine or motor. An aerodynamic line connected to the head and having a long beam axis having a pitch angle. A shaft extending between the engine or motor and the head and the aerodynamic line is mounted by the head so that the aerodynamic line has a pitch angle of about 5-45xc2x0 upward so that the string trimmer acts as a blower while still being capable of edging or trimming. The engine or motor is preferably constructed and operatively connected to the head so that the head has a speed of rotation of over 6000 rpm. A handle may be mounted on the shaft, having a first detented trigger having at least three operational positions mounted on the shaft for controlling by feel, the energy supply to the engine or motor, a second handle may be mounted on the engine or motor on the opposite portion thereof from the head, and a second detented trigger may be mounted on the second handle for alternatively controlling the energy supply to the engine or rotor. The system optionally may include a cart having at least three wheels and first and second adjustable arms mounting the shaft or engine or motor thereto so that the string trimmer is operational by utilizing the second trigger when mounted to the cart. The system may also further comprise an air scroll and debris shield for the head, which functions as a debris shield when the aerodynamic line is used to cut vegetation, and which functions as a directional air scroll when the trimmer is used as a blower.
According to another aspect of the present invention there is provided a method of operating a string trimmer having an engine or motor which is operative connected to a head, the head mounting aerodynamic line having a long beam axis having a pitch angle, the method comprising: (a) Operating the engine and the head in a first mode of operation where the pitch angle of the aerodynamic line is between about 0-10xc2x0 and the string trimmer is used for vegetation cutting. (b) Operating the string trimmer in a second mode where the pitch angle is between about 15-45xc2x0 upward and the string trimmer is used as a blower to provide a downward flow of air which clears cut vegetation in the surrounding area, and may provide a downward cooling flow of air. And, (c) operating the string trimmer in a third mode where the pitch angle is between 5-30xc2x0 downward to create an updraft for lawn mowing. For example, in the practice of the method (a) is practiced to rotate the head with an rpm of between 2500-6000 rpm, and (b) is practiced to rotate the head at an rpm of over 6000 rpm while (c) is practiced to rotate the head at an rpm between 3000-5000 rpm.
According to another aspect of the invention there is provided a bottom frame assembly mounting at least three wheels, each wheel rotatable about a substantially horizontal axis. First and second adjustable length arms, each arm mounted for rotation about a substantially vertical axis, and each arm having a free end. A clamp at the free end of the first arm for clamping a shaft of a string trimmer thereto. And a clamp, a flexible band, or flexible cord mounted at the free end of the second arm for operative attachment to the string trimmer so as to mount the string trimmer, with the clamp at the first arm free end, so as to facilitate utilization thereof for vegetation cutting and one or more other functions.
The cart as described above may further be constructed wherein at least three wheels comprising first and second back wheels, each mounted for rotation about a separate axle; and at least one front steerable wheel; and further comprising a support frame for supporting the arms to the bottom frame. The bottom frame and the support frame may consist essentially of hollow plastic tubes.
The cart may be provided in combination with a string trimmer, the string comprising: An engine or motor. A head operative connected to the engine or motor. An aerodynamic line connected to the head and having a long beam axis having a pitch angle. A shaft extending between the engine or motor and the head. And at least one handle, the at least one handle mounted on a portion of the string trimmer on an opposite side of the engine or motor from the head, and the at least one handle having a detented trigger for controlling the supply of energy to the engine or motor; and wherein at the end of the second arm a flexible band or cord is provided which wraps around the string trimmer shaft and allows essentially 360xc2x0 freedom of movement of the shaft with respect to the cart while still attaching the cart to the shaft. The handle may be used by an operator to control the string trimmer.
According to yet another aspect of the present invention a trimmer head for a string trimmer is provided comprising the following components: A body of relatively rigid material (e.g. of a metal, such as aluminum or zinc, or a rigid plastic). An aerodynamic line connected to the body and having a long beam axis and a twist with a living hinge and the head having a polar moment of inertia when used as a string trimmer head of between about 1.6-2.4 inch pounds second squared. For example the polar moment of inertia of the head may be approximately determined as follows:
Ihead=(2Mxcex8)/(xcfx8922xe2x88x92xcfx8912)xe2x88x92Ieng, 
wherein
Ieng=Total Inertia of Engine (Flywheel, Crank Shaft, Bearings, etc.),
Ihead=Total inertia of String Head,
xcfx89=angular velocity of head and engine,
M=Torque or Moment created by cutting Grass, and
xcex8=Total in cutting swath (in radians) where grass is being cut (maximum of 90 degrees or xcfx80/2).
The trimmer head may be operatively connected to a gasoline powered engine through gearing, the gearing providing a ratio of engine speed to the output speed of the head of about 1.5 or less; or may be operatively connected to a battery powered motor, and gearing, and wherein the gearing connects the battery powered motor to the head so that the ratio of motor speed to speed or rotation of the head is greater than 1.0. Lead or other dense weights may be mounted to or molded within the body spaced from the axis of rotation of the head, so that the head has a total weight of between about 8.4-24 ounces; or alternatively the head may be constructed initially so as to provide the desired moment of inertia, e. g. by adding metal or substantially rigid plastic thereto during construction, or by forming internal cavities which are then injected with molten lead or like heavier material than the material forming the head, and which form is solid when cooled.
It is the primary object of the present invention to provide enhanced functionality of a string trimmer, and optionally a cart which may further enhance the functionality thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.